1. Field of the Invention
The present invention relates to an electrophotographic photoreceptor comprising a protective layer containing a polyamide resin. More particularly, the present invention relates to an electrophotographic photoreceptor with improved electric and magnetic properties which has a protective layer containing a polyamide resin and a chelate compound where the chelate compound undergoes a crosslinking reaction with the polyamide resin.
2. Description of the Related Art
An electrophotographic photoreceptor is employed in electrophotographic image-forming apparatuses, such as facsimile machines, copiers, laser beam printers, CRT printers, LED printers, liquid crystal printers, and laser electrophotographic devices. Basically, in the electrophotographic image-forming apparatus, a photosensitive material is electrified and exposed to an image-forming light source to form an electrostatic latent image. Then, the image is developed with toner by applying a developing voltage, and after the toner image is transferred to a recording medium such as paper, the image is fixed thereon.
The electrophotographic photoreceptor comprises a photoconductive layer containing materials such as a charge generating material (CGM) and a charge transferring material (CTM) on an electrically conductive substrate. Generally, the electrophotographic photoreceptor contains an additional functional layer. For example, an undercoating layer is formed between the conductive substrate and the photoconductive layer. Alternatively, a protective layer is formed on the photoconductive layer.
The function of the protective layer (also referred to as surface protective layer; hereinafter collectively referred as to protective layer) is to prevent penetration of a liquid developing agent into the photoconductive layer and to prevent abrasion during the process of cleaning, etc. to protect the photoconductive layer.
In general, the protective layer contains a binder and, if necessary, an inorganic or organic filling agent dispersed therein. Various polymer resins can be used as the binder, and thermosetting resins having high mechanical strength, such as polyurethane resins, are commonly used.
Meanwhile, because polyamide resins have superior solvent resistance, electrical and magnetic characteristics compared to other thermosetting resins, the use of polyamide resins as a binder in the protective layer is being studied. U.S. Pat. No. 5,368,967 discloses the use of the polyamide resin as the binder in the protective layer.
However, polyamide resins generally have poor compatibility with other resins and are highly hydrophilic. Therefore, if the polyamide resin is contained as the binder in the protective layer, the adhesive property of the protective layer to the photoconductive layer decreases. In addition, the electrical characteristic of the protective layer is affected by humidity.
Japanese Patent Laid-Open Nos. Hei3-141365 and 2000-330313 disclose a method of using a polyamide resin after being crosslinked by a polymerizer or a crosslinking agent, in order to solve the problems of the protective layer containing the polyamide resin as the binder. However, this method has problems in that the storage stability of the coating liquid is poor since the crosslinking reaction between the polyamide resin and the polymerizer or the crosslinking agent occurs in a solution state at room temperature. The coating liquid is also difficult to use with the dipping method which is a coating method that typically provides good productivity.